(1) Field of the Invention
The present invention relates to a toner supply device for a developer unit provided with electrophotographic apparatus such as laser printers, copiers, facsimile machines and the like, in particular relates to a toner supply device which supplies the toner stored in the developer unit to a predetermined site therein with a conveying sheet whilst agitating the toner with a rotatable agitating element.
(2) Description of the Prior Art
Generally, in an electrophotographic printer, a developing device for creating toner images is provided with a toner supply device called a toner hopper. This toner hopper keeps spare toner in reserve and supplies fresh toner to the developing device as the toner is consumed by the development process. Also this toner hopper has an agitating element for agitating the toner therein and conveying the toner into the developing device. This agitating element is called an agitator or toner agitating shaft and functions to agitate the toner to thereby maintain the proper conveyance of toner and prevent the toner from sticking together in a mass or deteriorating in any other way.
This agitating element is generally formed of a relatively hard material such as metal, resin, etc., and is provided in the form of a rigid ladder structure. Hence, the agitating element has little elasticity or flexibility so that only the toner residing within the effective range of its rotational radius can be agitated and conveyed thereby. Therefore, when the toner in the toner hopper reduces to a certain extent, it becomes impossible to convey a sufficient amount of toner to the developing device because of a lower amount of the toner within the reach of the agitating element. Shortage in the amount of toner in the developing device will cause character voids and light print, producing difficulties in forming high quality images. Therefore, in order to keep the amount of toner in the toner hopper at a level greater than a certain amount, it has been necessary to frequently resupply the toner to the toner hopper, which degraded the operating rate of machine, running efficiency and running cost.
In order to solve the above problem, Japanese Patent Application Laid-Open Hei 6 No. 236110, for example, discloses a toner hopper in which a toner conveying element has a: rectangular conveying sheet having a strong elasticity at the distal end thereof so that the sheet will be able to slide over the inner wall surface of the toner hopper. This arrangement enables a sufficient amount of toner to be brought into the developing device even if only a low amount of toner remains in the toner hopper and makes possible effective use of the toner in the toner hopper and can improve the machine operating rate.
FIG. 1A shows a configurational example of this toner hopper 2. Toner hopper 2 in this figure has a toner container 9 for holding the toner and is connected to an unillustrated developing device arranged opposing the photosensitive member by a toner supply portion 10 with a sponge roller 10a arranged therein. In this developing device, an unillustrated internal roller is rotationally driven in a predetermined direction by driving means. Toner hopper 2 is enclosed by a top plate 14, a wall surface (side wall) 22 of toner container 9 and a wall surface 23 of toner supply portion 10. FIG. 2A shows shapes of wall surface 22 of toner container 9 and wall surface 23 of toner supply portion 10. Toner container 9 is a receptacle of an approximately rectangular parallelepiped, defined by wall surface 22, unillustrated side walls arranged perpendicular to the wall surface 22 and top plate 14. Toner supply portion 10 is connected to the upper side part of toner container 9 and is enclosed by a groove defined by wall surface 23 of a semi-cylindrical or other shape and top plate 14. An agitating element 11 and conveying sheet 12 as shown in FIG. 2B are arranged in the toner container 9 thus configured.
Agitating element 11 is provided so as to be rotated about an agitating shaft 11a which extends in parallel with the rotational axis of the photosensitive drum (the direction indicated by the arrow W in the drawing). In order to perform efficient toner conveyance, conveying sheet 12 made up of a soft resilient material, such as a PET sheet or the like is fixed at its proximal side 12b to the distal part of agitating element 11 away from the rotational axis, by double-sided adhesive tape or the like. The distal end, designated at 12a, of conveying sheet 12 is formed in parallel with the axial line of agitating shaft 11a and bent in the rotating direction. This shape enhances the rigidity of the distal part of conveying sheet 12 hence makes it possible to convey the toner uniformly toward the developing device. When this agitating element 11 is rotated, conveying sheet 12 rotates with its distal part 12a kept in contact with the inner wall (the inner surface of top plate 14 and the inner wall surface 22) of toner container 9 while stirring the toner in the toner container 9 and conveying it toward the developing device.
FIGS. 1A to 1F show the actions in the thus configured toner hopper 2 during toner supply. In the drawings, as agitating shaft 11a rotates clockwise, conveying sheet 12 deforms holding and conveying the toner with its distal part 12a being in sliding contact with the inner wall surface of toner container 9, as shown in FIGS. 1A and 1B. Then, as shown in FIGS. 1C and 1D, the held toner is supplied to toner supply portion 10. Thereafter, conveying sheet 12 moves over the inner side of top plate 14 and transfers its contact point from the sliding movement over top plate 14 to the sliding movement over wall surface 22 as shown in FIGS. 1E to 1F, restarting a next toner holding and conveying cycle.
Since in the above toner hopper 2 conveying sheet 12 is made to slide over the inner wall of toner container 9 in order to make effective use of the toner, the sheet produces contact noise with the inner wall, increasing the noise level. Of such contact noise, the grating sounds arising while the sheet is sliding over the inner wall are not so intense when a relatively large amount of toner is held because the noise is absorbed by the toner. However, as the amount of toner decreases the grating sounds, instead of being absorbed, are heard outside, reaching the user as uncomfortable noise.
One factor that causes the above-described contact noise is a recoiling or grating sound (to called a colliding sound) which arises when conveying sheet 12 abruptly reverts itself back to the original shape due to elastic force and sharply collides with wall surface 22 in the inner space at the meeting point between top plate 14 and wall surface 22 during the action where conveying sheet 12 moves from the state shown in FIG. 1E to the state shown in FIG. 1F, that is, the sheet transfers its contact point from the sliding movement over top plate 14 to the sliding movement over wall surface 22. As the rigidity or mechanical strength of the conveying sheet is enhanced in order to provide more stabilized toner conveyance, this colliding sound becomes more liable to occur and acts as the main source, or cause of the noise. Recently in situations where noise reduction in printer technologies has become more important to meet various needs, there has been a strong demand for sufficient enough countermeasures against noisy sounds of this kind.
Further, there is a risk of the distal part 12a of conveying sheet 12 being damaged because the sheet is pressed against the inner wall of toner container 9 and greatly flexed and deformed at that part while agitating element 11 is being rotated. In order to avoid this risk, cutouts 12c of various shapes may be formed in the distal part of conveying sheet 12 as shown in FIGS. 3A to 3D. A similar manipulation has been disclosed also in Japanese Patent Application Laid-Open Hei 9 No. 244368. If cutouts 12c . . . as shown in the same drawings are formed, the area of conveying sheet 12 in sliding contact with the inner wall of toner-container 9 decreases so that reduction of the grating sound can be expected. Further, the area of conveying sheet 12 colliding with wall surface 22 when the sheet transfers its contact point from the sliding movement over top plate 14 to the sliding movement over wall surface 22 decreases so that the aforementioned colliding sound may be reduced to a certain extent. However, the provision of cutouts 12c in conveying sheet 12 will reduce its holding capacity of the toner to a level lower than necessary, making it difficult to uniformly convey the toner from toner container 9 toward the developing device. This may cause degradation of image quality such as light print or low contrast, etc. Also, the shape of conveying sheet 12 becomes complicated lowering profitability.
The present invention has been devised in view of the above problems, it is therefore an object of the present invention to provide a toner supply device which can reduce the uncomfortable noise generated from the conveying sheet colliding with the inner wall while keeping high enough conveying capability of the toner.
In order to achieve the above object, the present invention is characterized in that a slider element having a low frictional resistance is attached to the distal part of the conveying sheet. That is, a toner supply device, according to the present invention includes: an agitating element for agitating the toner in a toner container; a conveying sheet attached to one end portion of the agitating element and rotating with the agitating element to convey the toner to a predetermined position, wherein the distance from the proximal to the distal end of the conveying sheet is greater than the rotational radius of the agitating element and is set so that the distal end of the conveying sheet is put in sliding contact with the inner wall of the toner container by the agitating element being rotated; and a slider element provided at the distal end of the conveying sheet.
Since the conveying sheet is long enough to come into sliding contact with the inner wall of the toner container, it is possible to improve the toner usage efficiency. The provision of the slider element having a low frictional resistance at the distal end of the conveying sheet makes it possible to reduce the frictional force acting on the inner wall of the toner container during sliding movement. With this arrangement, even when the toner container is filled with a relatively large amount of toner, it is possible to smoothly convey the toner with the conveying sheet while suppressing the stress acting on the toner. Further, when grating sounds become easy to arise as the amount of toner in the toner container has decreased, it is possible to reduce high frequency sounds arising due to sliding contact and hence reduce uncomfortable noise. As a result, it is possible to improve the toner supply device and hence the total quality of the electrophotographic apparatus using it.
The slider element having a low frictional resistance to be attached to the distal end of the conveying sheet preferably has a coefficient of dynamic friction of 0.40 or below, preferably about 0.20 (ASTM D-1894) and a coefficient of static friction of about 0.28 (ASTM D-1894).
Since the slider element is made of a soft resilient material having a rebound resilience of 80% or below, the slider element will deform fitting along the aspect of the inner wall of the toner container when it is put in contact with that inner wall. Therefore, it is possible to keep the frictional resistance low during sliding movement.
The material of the slider element meeting these conditions should be a soft resilient material (a soft and restorable material) with a lower resistance of friction and examples includes: fluororesin tape; ultrahigh molecular polyamide resin film (xe2x80x98POLYSLIDERxe2x80x99 a product of ASAHI POLYSLIDER Co. Ltd., etc.); ultrahigh molecular polyethylene resin film with carbon filaments blended therein (xe2x80x98PENRON C954xe2x80x99 a product of NTN Corporation, etc.,) and the like. Particularly, polyolefin resin substrate film etc., having a coefficient of dynamic friction of 0.20 (ASTM D-1894) and a coefficient of static friction of about 0.28 (ASTM D-1894) can be preferably used.
In this case, setting the thickness of the slider element smaller than that of the conveying sheet makes it easy for the slider element to deform fitting along the aspect of the inner wall. Further, this thinness is advantageous for frictional resistance. Smallness of the absolute value of the coefficient of dynamic friction and the time-dependent increase of the dynamic friction makes it possible to reduce the loads on the drive system of the agitating element and the stress acting on the toner. Specifically, the thickness of the slider element should be about 30 to 80 xcexcm or preferably falls within the range of 50xc2x110 xcexcm.
Because conveyance of the toner is performed by the conveying sheet, there is no need to enhance the strength and rigidity of the slider element, so that no problem of the durability will occur when a thin soft resilient material is used.
Provision of cutouts in the distal part of the slider element makes smaller the contact area between the slider element and the inner wall surface of the toner container. Accordingly, the contact friction can be reduced so that it is possible to enhance the smoothness of the movement of the agitating element and conveying sheet, which leads to efficient conveyance of the toner. As examples of the cutouts capable of reducing the contact friction, a rectangular pattern, wavy pattern, saw-toothed pattern, triangular pattern and other patterns can be adopted.
Alternatively, provision of a series of openings along the distal part of the slider element allows part of the toner to escape through the openings. Therefore, it is possible to reduce the amount of toner scooped by the slider element, so that the resistance (the pressure of the toner) acting on the conveying sheet can be reduced, thus making it possible to smoothen the movement of the conveying sheet and agitating element. The openings are preferably arranged at regular intervals on the slider element in consideration of pressure balance. The openings are preferably provided in a rectangular or circular configuration.
When the slider element is folded in an approximately U-shape and fixed to the conveying sheet by both ends thereof so that the bent part extends beyond the distal part of the conveying sheet and covers the distal part of the conveying sheet, this enables the bent surface of the slider element come into contact with the inner wall of the toner container, hence the state of contact can be stabilized thus making it possible to smoothen the movement of the conveying sheet and agitating element. Further, since the slider element can be fixed firmly by its both ends, it is possible to prevent the slider element from dropping or peeling, thus leading to improvement of reliability.
Moreover, when the distal part of the conveying sheet is bent in the rotational direction to form a bent portion while a slider element is attached to the bent portion so that it extends beyond the bent portion, the conveying sheet can be improved in rigidity and conveyance of the toner. In this case, if a slider element is attached to the reverse side (the side opposite to the rotational direction) of the bent portion, the bent portion would come first into contact with the inner wall surface of the toner container before the slider element. So this arrangement cannot reduce the frictional resistance during sliding movement. Therefore, the slider element is preferred to be attached on the front side of the bent portion, i.e., on the front side in the rotational direction. With this arrangement, the slider element will come first into contact with the inner wall, hence it is possible to reduce the frictional resistance during sliding movement.
In accordance with the present invention, in order to attain the above object, a toner supply device includes: a toner container for holding the toner in a receptacle with a top plate; an agitating element which is rotationally driven in a predetermined direction to agitate the toner in a toner container; a conveying sheet joined to the agitating element and rotating with rotation of the agitating element whilst being deformed with its distal end put in sliding contact with, at least, the top plate of the toner container, the side wall connected to the top plate and the inner wall in contact with the toner, to thereby scoop up and bring the toner to a predetermined position, and is characterized in that curved surface forming member for defining a curved surface smoothly connecting between the top plate surface and the side wall surface is provided at the meeting position between the top plate and the side wall inside the toner container so that the distal end of the deformed conveying sheet comes at least in part into sliding contact with the curved surface forming sites of the curved surface forming member and the full-length of the distal end of the conveying sheet approximately moves over the curved surface.
According to the above invention, the curved surface forming member is provided at the meeting position between the top plate and the side wall inside the toner container. Therefore, when the conveying sheet transfers its contact point from the sliding movement over the top plate to the sliding movement over side wall, the full-length of the distal end of the conveying sheet, as it being deformed, will move over the curved surface defined by the curved surface forming member. The curved surface forming member is made up of either a single component having the curved surface or multiple components defining the surfaces or lines which constitute part of the curved surface.
Accordingly, the deformation of the conveying sheet during the sliding movement over the top plate will not be released abruptly on the interior side of the toner container after the meeting point between the top plate and the side wall. Therefore, the conveying sheet smoothly transfers its contact point from the sliding movement over the top plate to the sliding movement over side wall, whereby it is possible to avoid the conveying sheet colliding with the side wall. Since the conveying sheet need not to have any cutouts and the distal part of the conveying sheet comes into sliding contact the inner wall contacting with the toner, it is possible to hold and convey a sufficient amount of toner in a stable manner.
In this way, it is possible to suppress generation of uncomfortable noise resulting f rom collision of the conveying sheet against the inner wall whilst keeping its capability of conveying a sufficient amount of toner.
Another toner supply device according to the present invention is characterized in that the curved surface forming member is comprised of a multiple number of plate-like ribs, arranged apart from one another in the direction perpendicular to the direction of the sliding movement of the conveying sheet, each rib being projected inward in the toner container from the top plate or from the side wall with its width put in the direction of the spacing and the end portions of the ribs on the interior side of the toner container are adapted to function as the curved surface forming sites.
According to the above invention, since the curved surface forming member is composed of the ribs as above and the end portions on the interior side of the toner container constitute the curved surface forming sites, only limited part of the distal end of the conveying sheet will come in contact with the curved surface forming member. Therefore, this configuration makes it possible to minimize damage to the conveying sheet due to its sliding movement over the curved surface forming member, stress acting on the toner and generation of grating sounds. Further, since the curved surface forming member is constituted by a multiple number of ribs, each being small, production with a metal die can be simplified.
Further, a toner supply device according to the present invention is characterized in that the end portion of each rib on the interior side of the toner container has an end formed of a strip of curved surface that constitutes part of the curved surface and the ridges located at both sides of each end portion with respect to the spacing direction of the ribs are rounded.
According to the above invention, since the end portions of the ribs on the interior side of the toner container or the strips of curved surfaces forming part of the curved surface are adapted to work as the curved surface forming sites while the corners located at both sides of each end portion of the rib with respect to the spacing direction of the ribs are rounded, it is possible to avoid interference of the distal end of the conveying sheet with the ribs. As a result, the distal end of the conveying sheet can smoothly move under reduced resistance to movement, so that it is possible to inhibit the conveying sheet from being damaged by the sliding movement over the curved surface forming member, the toner from being stressed and generation of grating sounds.
A toner supply device according to another aspect of the present invention is characterized in that the end portion of each rib on the interior side of the toner container has a curved ridgeline end that extends in the sliding direction of the conveying sheet and constitutes part of the curved surface and each end is rounded with respect to the direction of the spacing and the cross section of the distal end of each rib cut along a plane perpendicular to the end is angled or tapered on the distal side.
According to the above invention, since the end portions of the ribs on the interior side of the toner container are shaped as the curved ridgelines forming part of the above curved surface and hence are made to function as the curved surface forming sites while the end portions are rounded with respect to the spacing direction of the ribs, it is possible to avoid interference of the distal end of the conveying sheet with the ribs and it is possible to reduce the area of the conveying sheet which comes in sliding contact with the ribs. As a result, the distal end of the conveying sheet can move more smoothly under a further reduced resistance to movement, this configuration, therefore, is more effective in inhibiting the conveying sheet from being damaged due to its sliding movement over the curved surface forming member, the toner from being stressed and generation of grating sounds. Further, the configuration of the ribs being angled or tapered in section provides improvement in the durability of the metal die for producing the ribs of this shape, thus contributing to mass production and low cost.
A toner supply device according to still another aspect of the present invention is characterized in that the end portion of each rib on the interior side of the toner container has a curved ridgeline end that extends in the sliding direction of the conveying sheet and constitutes part of the curved surface and the cross section of the distal end of each rib cut along a plane perpendicular to the end is approximately semicircular on the distal side.
According to the above invention, since the end portions of the ribs on the interior side of the toner container are shaped as the curved ridgelines forming part of the above curved surface and hence are made to function as the curved surface forming sites while the section of the ribs are formed to be approximately semicircular or the end portions are rounded with respect to the spacing direction of the ribs it is possible to avoid interference of the distal end of the conveying sheet with the ribs and it is possible to reduce the area of the conveying sheet which comes in sliding contact with the ribs. As a result, the distal end of the conveying sheet can move more smoothly under a further reduced resistance to movement, this configuration, therefore, is more effective in inhibiting the conveying sheet from being damaged due to its sliding movement over the curved surface forming member, the toner from being stressed and generation of grating sounds. Further, the configuration of the ribs being approximately semicircular in section provides marked improvement in the durability of the metal die for producing the ribs of this shape, thus further contributing to mass production and low cost.
Application of the conveying sheet with its distal end attached with any of the slider elements described above and the curved surface forming member in combination to a toner supply device makes it possible to obtain the combined effects and advantages as described above.